1. Field of the Invention
This invention relates to material-handling vehicles and, more particularly, to a double articulated vehicle with means for interconnecting the steering of the front and rear frames.
2. Description of the Prior Art
Double articulated vehicles broadly have been known but have not been widely used. Possible reasons for the limited use could be due to the problems associated with the complex systems for controlling the steering of the vehicle. One such system provides for using a hydraulic cylinder having a rod which requires that the front wheels be tracked to align with the rear wheels. The rod is mounted on one side of the centerline of the vehicle and is connected to bell cranks on the front and rear frames such that the front wheels will always lie in a plane parallel to the plane of the wheels of the rear frame.
In another form of double articulated vehicle, two pairs of hydraulic rams are connected between the rear unit and a central unit and between the central unit and a front unit for steering the vehicle. Extendable follow-up valves are used to control the flow of hydraulic fluid to the rams for steering the front and rear units through equal angles. With the number of hydraulic rams, the hydraulic piping and the hydraulic valves and controls, the possibility of malfunction of one or more parts of the system is great, resulting in failure of the steering of the vehicle. Leaking of one ram is sufficient to cause failure of the system.
Another prior art device uses two pairs of hydraulic rams between the front, center and rear units with a follow-up extendable link diagonally connected between the front and rear units to sense and time the angular movement of the units. Once again, the number of cylinders, piping and controls are such that a failure or malfunction of one throws off the entire system resulting in loss of control of the steering of the vehicle.